The packerhead or rollerhead process or method of concrete pipe formation is widely accepted as the least expensive and most efficient method of concrete pipe formation. Generally speaking, the apparatus for forming pipe by this method includes:
1. An outer, vertically disposed, longitudinally hinged, bell-end down mold or jacket, for shaping or forming the outer surface of a section of pipe. The mold or jacket alternatively may be bell-end up.
2. An interior, vertically reciprocal rotary packerhead, same concentrically disposed with respect to the mold and adapted to form the interior surface of the section of pipe. The completed pipe section consists of a bell or female end, first formed, the cylindrical body of the pipe, second formed thereabove, and a male end, last formed at the upper, terminal end of the pipe body. The sequence of steps varies on the end formed first. That described here and below is bell-end down.
The sequential steps of concrete pipe section formation by this process are as follows. The jacket is vertically situated, bell or female end down. The rotary packerhead is lowered concentrically therewithin, to the bottom of the mold. Concrete is then introduced and the packerhead shaft rotated so as to form the bell end of the pipe. The mold may be vibrated at this time to eliminate any bell end voids. Once the bell end is formed, the packerhead is raised and rotated while concrete is continuously introduced into the mold whereby to form the cylindrical body of the pipe above the bell. When the formation of the entire vertical height of the pipe section is completed, an additional one or more passes of the packerhead centrally of the mold and the formed pipe may be employed to finish the interior surface of the pipe. Thereafter, the packerhead is removed and the mold containing the completed pipe is moved for curing, whereupon a new mold (empty) is provided on site and the process repeated.
Although the pipe is of sufficient strength that it will support its own weight after formation, it must be cured to obtain full strength. That mold which contains a newly formed pipe is transferred from the pipe forming zone to the curing area where the mold is removed from the pipe for recycling for use in forming another pipe.